public function testChangeMessageAsyncMode()
 {
     $this->assertFalse($this->_message->isAsync());
     $this->assertInstanceOf('\\nickcv\\mandrill\\Message', $this->_message->enableAsync());
     $this->assertTrue($this->_message->isAsync());
     $this->assertInstanceOf('\\nickcv\\mandrill\\Message', $this->_message->disableAsync());
     $this->assertFalse($this->_message->isAsync());
 }